The present invention relates generally to sewing machines and sewing processes, and more particularly to a sewing machine or process for positioning a stitching line within a predetermined tolerance.
Over the years, engineers have developed a great variety of electronic sewing machines. Devices having automatic control and sensing functions have been conceived, many meeting with great success, however, designers are always searching for improvements in stitching precision and accuracy. For instance, myriad circumstances exist in which it is desirable to place a line of stitches within a minimum distance from a selected stitching reference. When following a sewing pattern that has been printed, drawn, or even projected onto a workpiece, it may be crucial for success of the project that the stitches deviate no more than a given xe2x80x9ctolerancexe2x80x9d from their intended position. One instance in which it is particularly desirable to position stitches precisely is when tracing an edge of a workpiece, for example when joining two overlaying pieces of fabric at their respective edges. If the operator sews the pieces too close to the edge, the seam may be too weak, allowing the stitches to pull out, and the fabric pieces to separate. Where two pieces of fabric tightly enclose a packed interior, for instance a filled cushion, this can be particularly problematic. If the operator positions the stitches too far from the workpiece edges, interior volume can be sacrificed, and cosmetic appearance compromised.
One device directed to positioning stitches along a workpiece edge is disclosed in U.S. Pat. No. 5,042,410 to Nakashima. Nakashima provides a bed and a reciprocable sewing needle mounted in a swinging mechanism for swinging the needle in a direction across the feeding direction of the workpiece. Further, Nakashima provides a detector for detecting the fabric edge, and a margin setting mechanism for setting the appropriate sewing margin from the edge of the workpiece. Based on the needle position and the workpiece edge position, a reference stitching line can be projected by a light projector onto the workpiece, serving as a guideline for positioning the fabric edge and/or the stitching line. Thus, the machine operator can manually control the position of the workpiece, following the projected stitching line.
Accompanying improvements in stitching precision have been developments in detecting and informing an operator when erroneous or undesirable machine conditions are encountered. In certain of these machines, a device is illuminated to signal the detection of an erroneous condition or event to a machine operator. U.S. Pat. No. 5,078,067 to Nakashima is directed to informing an operator of undesirable operating conditions. Nakashima provides a sewing machine with illuminating means for illuminating with light of different colors the sewing area on which an operator is working. Nakashima is relatively complex, and requires a separate motor to rotate a series of colored filters in front of a light source to change the color of projected light.
U.S. Pat. No. 6,138,594 to Kito et al is entitled Electronically Controlled Sewing Machine, and provides an informing device that visually (or aurally) informs a user which of several operations of the sewing machine is possible or impossible by illuminating LEDs of different colors to correspond to different conditions. One such indication communicated to the operator is whether the position of the sewing needle is within a desired position range above a needle plate. Kito, however, is relatively complex.
In one aspect, the present invention provides a sewing machine. The machine has a machine body affixed to a mounting plate and a reciprocable sewing needle attached to the machine body. The needle is movable between a retracted position and an extended position at which a needle tip pierces a laterally moving workpiece along a stitching line and passes a sewing strand or thread through the workpiece. A detector is also provided for determining a lateral position of the needle relative to the workpiece. The present invention also provides a plurality of lamps operably linked to the detector, wherein illumination of one of the plurality of lamps occurs at a first condition wherein a stitching line is positioned less than a predetermined tolerance distance from a selected position. Illumination of a second of the plurality of lamps occurs at a second condition wherein the stitching line is positioned greater than the predetermined tolerance distance from the selected position.
In another aspect, the present invention provides a method of positioning a stitching line within a predetermined range of distances from a workpiece edge. The method includes the steps of selecting a distance range for positioning a stitching line laterally of a workpiece edge, the distance range comprising a minimum distance and a maximum distance. The method also includes the step of feeding a workpiece past a reciprocable needle in a sewing machine, wherein the sewing machine is operable to serially pass an end of the needle through the translating workpiece, forming stitches therethrough, and the step of detecting a lateral position of the stitches relative to an edge of the workpiece. The method also includes the steps of operating an illumination means to a first state when the stitches are positioned greater than the minimum distance and less than the maximum distance from the workpiece edge, and operating the illumination means to a second state when the stitches are positioned less than the minimum distance or greater than the maximum distance from the workpiece edge.